To meet demands for faster processors and higher capacity memories, integrated circuit (IC) designers are focusing on decreasing the minimum feature size within integrated circuits. By minimizing the feature size within an integrated circuit, device density on an individual chip increases exponentially, as desired, enabling designers to meet the demands imposed on them. One such feature is the so-called contact aperture, or “contact,” which is typically a circular hole extending through a layer of dielectric material to a structure formed on or in an underlying semiconductor substrate.
As circuit component structures, including contacts, enter the sub-half micron range of dimensions, tolerances become more critical and demand more precise process parameters. For example, sub-half micron contacts must hold the top contact diameter (top CD) within a narrow tolerance band while a high aspect ratio contact is etched through a dielectric layer, and the contact itself must exhibit a substantially cylindrical cross section (i.e., little taper) to achieve an effective contact area with the underlying substrate. As used herein, the term “high aspect ratio” as applied to contact structures is currently contemplated to indicate a depth to width, or diameter, ratio of about five to one or more (≧5:1). In addition to contacts, it is also necessary in some instances to etch high aspect ratio sub-half micron width lines or trenches through dielectric layers, and fabrication of these structures demands similar precision. Mixtures of these structures, i.e., holes and trenches, are common in semiconductor fabrication, particularly in those using dual-damascene techniques.
It is highly desirable to etch high aspect ratio contacts through a layer of doped silicon dioxide such as borophosphosilicate glass, or BPSG, and sometimes through additional layers such as other oxides, silicon nitride or inorganic, dielectric anti-reflective coating (DARC) films between the mask and the substrate silicon. Desired contact structures to be achieved would have a minimum nominal depth of 1–2 μm, an aspect ratio of approximately 5:1 to 10:1 or higher, and a profile angle of greater than approximately 87° as measured from a horizontal plane of the substrate. High selectivity for BPSG to the substrate silicon is preferred, as is the ability to etch the other films, such as the aforementioned silicon nitride and DARC films.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods for producing high aspect ratio structures.